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We usually hear that an invasive species has brought with it a disease which it itself shrugs off easily, but which then decimates the local population which has never encountered it before. It's a very common story. But it doesn't make sense to me. Surely it should be far more common for the reverse to happen? Surely a newly arriving species has to face not just one or two new things in the new environment, from one or two new individuals, but an entire environment coming at it from every direction with hundreds of viruses, bacteria and competitors it has never come across before. So how come the story is always that the invading species kills off the locals, when you would expect the invading species to have hundreds of totally new threats and strange foods to handle, would be unable to cope, and would die out?

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So how come the story is always that the invading species kills off the locals, when you would expect the invading species to have hundreds of totally new threats and strange foods to handle, would be unable to cope, and would die out?

There is a problem of observation bias for these two scenarios. In the first scenario a few members of an invasive species enter a new range, transmit a novel disease to the pre-existing species, which suffers a massive (easily observable) die off. In the second scenario, a few members of an invasive species enter a new range, catch a local disease, and die in short order (unobserved and unnoticed).

In other words, a few individual deaths from any cause will generally go unnoticed. Thousands or millions of deaths of deaths from a novel disease are more likely to attract attention.

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  • $\begingroup$ That's a good answer, thanks. $\endgroup$ – Stephen F Dec 5 '19 at 9:34
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Charles is correct. You might want to look up 'failure to thrive', and 'introduction failed' when humans tried to introduce new species (the existing environment ate them up), and it didn't work out.

We tend to record successes, and bury failures.

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